While the wayfaring playboy Willmore is a literal "rover" of the world who moves from port to port and lover to lover, Aphra Behn's title remains ambiguous regarding exactly which character it refers to. In fact, there is a strong critical case to make for the titular rover actually referring to Hellena's character, especially since author Behn places the inner lives, fortunes, and sympathies of her female characters at the forefront of the play.
The main way Hellena is a true "rover" is in the primary definition of the term as someone who strays or wanders their own path, similarly to how it applies to her male foil Willmore. Although young women in the seventeenth century, as throughout most of history, rarely had the freedom to choose lives of adventure and self-gratification, Hellena nonetheless departs from the narrow path proscribed for her by social custom and family honor.
Instead of yielding to her brother's expectations for her to spend her life in silent, cloistered devotion, the willful and self-determined Hellena rejects the path forced on her to veer off on her own in pursuit of love and marriage on her own terms. In that regard, she enters forbidden, unknown, and yet tantalizing territory where few girls of Hellena's privileged status were free to venture.
Because Hellena's "roving" away from the patriarchal strictures of upper-class European society in pursuit of an authentic existence is an example of something that happened so rarely in Behn's world, Hellena's actions are more extraordinary. For this reason, it can be argued that the title refers to Hellena as much or more than to Willmore.
Several characters in Aphra Behn's play The Rover might actually merit such a title. A rover is generally someone who travels off the beaten path, who goes off on their own way to follow their own pursuits.
Many readers assume that Willmore is the title character, the Rover extraordinaire, for he literally roves about the world as a cavalier in exile and a naval captain. He also has a roving eye that looks toward one woman after another. What's more, he generally doesn't stop at just looking. He chases women lustfully.
Willmore, however, isn't the only character in the play who might be labeled as a “rover.” Many critics believe that Hellena is a good choice to claim the title. Hellena's family has designated her to become a nun, but she is much more interested in looking for love. Hellena is unconventional and bold. She doesn't hesitate to disguise herself to go to the carnival as a gypsy girl. She is highly attracted to Willmore, but she will not allow him to seduce her. Her self-respect is too great for that, and she won't fall into the trap other women end up in. By the end of the play, though, Hellena is engaged to Willmore, but the two again follow a divergent road, for they vow to be unfaithful to each other. Perhaps both of them are rovers in the end.
Other characters that might earn the title of “rover” include the prostitute Angelica, who is certainly living an unconventional lifestyle and uses a series of interesting and unorthodox methods of trying to get what she wants (namely Willmore). Antonio, too, is a rover of sorts, for while he claims to want to marry Florinda, he also wants to sleep with Angelica. While Florinda remains faithful to her true love, Belvile (and he to her), she also dashes all over the city in disguise and gets into plenty of scrapes. She is certainly not pursuing her love in any normal way, and this might make her, too, a rover. Even Belvile might earn the title through his escapades, including disguising himself as Antonio at one point.
Generally speaking, critics tend to regard Hellena as the rover of the title because she's a free-spirit who marries for love. At the time when the play was written, women—especially women of Hellena's social class—didn't have much choice in whom they married. Marriages among the upper-classes were often little more than glorified diplomatic treaties or business deals. Love seldom entered into the equation for the interested parties.
Hellena is destined for a convent thanks to her tyrannical father. So her love affair with Willmore represents what would've been seen at the time as a shocking challenge to prevailing convention. The methods that Hellena employs to get her man are also subversive. Putting on the disguise of a page is a particularly transgressive act of cross-dressing that allows Hellena to exercise far more autonomy and moral agency than she ever would as a woman in Restoration society.
Broadly speaking, there are two reasons why critics might think that Hellena is the rover who gives the play its title. The first is internal to the play: Hellena roves more widely from her assigned course than anyone else. Wilmore takes few social risks with his actions and attitudes; Hellena risks much. The second is historical/biographical; Hellena makes independent choices somewhat similar to Behn's own, and so one might think that Behn might make such a character the namesake of the play.